III-V heterojunction field effect transistor

ABSTRACT

Disclosed is a novel III-V heterojunction field effect transistor comprising a substrate layer, a first semiconductor layer, a second semiconductor layer, a drain electrode, a source electrode, a gate electrode, a first dielectric layer, second dielectric layers and the like, wherein the first semiconductor layer has a greater bandgap compared with the second semiconductor layer, and the second semiconductor layer and the first semiconductor layer are combined to form a heterostructure. The thickness of the first semiconductor layer is not greater than the critical thickness of two-dimensional electron gas formed in a heterojunction channel, and thus natural 2DEG in the heterojunction channel is depleted. The novel III-V heterojunction field effect transistor has the advantages of being simple in structure, simple in preparation process, stable in performance, high in reliability and the like.

BACKGROUND OF THE INVENTION Technical Field

The application relates to the technical field of semiconductor devices,in particular to a novel III-V heterojunction field effect transistor.

Description of Related Art

Certain binary or ternary compounds (even polycompounds) prepared fromgroup-III elements and group-V elements have spontaneous polarizationand piezoelectric polarization effects, and when the binary or ternarycompounds (even the polycompounds) are combined to form a heterojunction(such as AlGaN/GaN), high-concentration two-dimensional electron gas(2DEG) can be formed on a heterojunction interface, and a device usingthe 2DEG on the heterojunction interface as a channel is called aheterojunction field effect transistor (HFET) and can also be called ahigh electron mobility transistor (HEMT).

The HFET device has the characteristics of high electron mobility, highoperating frequency and high efficiency and has extremely importantapplication in the fields of radio frequency power amplifier and powersemiconductor electronics. However, up to now, taking an AlGaN/GaN HFETas an example, the HFET device has a natural defect in that due toextremely powerful spontaneous polarization and piezoelectricpolarization, high-concentration 2DEG is formed on the heterojunctioninterface in the absence of any external voltage, and the HFET device isnaturally depleted (normally on). The application of the HFET device toa logical circuit and a power electronic circuit is limited by thedefect of the HFET device, the logical circuit needs logic compensationbased on a enhancement-mode (normally off) and a depleted (normally on)device, and for ensuring safety and saving energy, the power electroniccircuit also needs enhancement-mode (normally off) devices. As is shownin FIG. 1, which is a sectional view of the depleted III-V HFET devicein the prior art, the depleted III-V HFET device comprises a substratelayer 9, a second semiconductor layer 10, a first semiconductor layer14, two-dimensional electron gas 11, a drain electrode 12, a sourceelectrode 13, a gate dielectric layer 15 and a gate electrode 16,wherein the second semiconductor layer 10 and the first semiconductorlayer 14 form a heterostructure, and as the thickness of the firstsemiconductor layer 14 exceeds the critical thickness in the prior art,2DEG exists on a heterojunction interface, namely the interface betweenthe first semiconductor layer and the second semiconductor layer, due topiezoelectric polarization and spontaneous polarization of the materialsystem under the condition that no external voltage is applied.

In the prior art, an enhancement-mode HFET device is obtained generallythrough the following several methods:

An F⁻ ion implantation technique for a channel below a gate electrode:specifically, F negative ions are implantation into a barrier layerbelow the gate electrode, electrons in the channel below the gateelectrode are depleted by means of the negative potential, and apositive threshold voltage of the device (namely the enhancement-modedevice) is realized.

A trench gate technique: specifically, a barrier layer below a gateelectrode is partially thinned through the dry etching technique, and2DEG below the gate electrode is depleted when the thickness of thebarrier layer is smaller than the critical thickness. 2DEG can beinduced again only when the gate voltage is higher than a certainvoltage, and thus the enhancement-mode device is realized.

As for a device adopting a P—AlGaN layer, the p-AlGaN layer isadditionally arranged below a gate electrode, and 2DEG in a channel isdepleted under the balancing effect of an energy band.

The techniques mentioned above have different disadvantages;specifically, the F-ion implantation technique has problems in theaspects of ensuring reliability and obtaining a larger threshold value,the trench gate technique has large difficulties in the aspect ofprocess control, and the P—AlGaN technique has the defects of difficultmaterial growth, low switching frequency of the device and the like.

Therefore, it is truly necessary to make a study to provide a scheme toovercome the defects in the prior art.

BRIEF SUMMARY OF THE INVENTION

On this account, the present application mainly aims to provide a novelIII-V heterojunction field effect transistor so as to solve the aboveproblems.

One embodiment of the present application provides a novel III-Vheterojunction field effect transistor which comprises a substratelayer, a second semiconductor layer, a first semiconductor layer, adrain electrode, a source electrode, a first dielectric layer, seconddielectric layers and a gate electrode, wherein,

the second semiconductor layer is formed on the substrate layer, thedrain electrode and the source electrode are constructed on the secondsemiconductor layer, and the drain electrode and the source electrodeare connected through the first semiconductor layer and are in Ohmiccontact with the first semiconductor layer, so that a channel is formed;compared with the second semiconductor layer, the first semiconductorlayer has a greater bandgap;

the second semiconductor layer and the first semiconductor layer arecombined to form a heterostructure; the thickness of the firstsemiconductor layer is not greater than the critical thickness of 2DEGformed on the heterostructure, and thus natural 2DEG in theheterostructure is depleted;

the first dielectric layer is further arranged on the surface of thefirst semiconductor layer, the gate electrode is arranged on the firstdielectric layer and covers the channel in the full length direction,and the two edges of the gate electrode extend out of the edges of thesides, close to the channel, of the drain electrode and the sourceelectrode respectively; the second dielectric layers are arrangedbetween the gate electrode and the drain electrode as well as betweenthe gate electrode and the source electrode.

One embodiment of the present application provides a novel III-Vheterojunction field effect transistor which comprises a substratelayer, a first semiconductor layer, a second semiconductor layer, adielectric template layer, a drain electrode, a source electrode, afirst dielectric layer, second dielectric layers and a gate electrode,wherein,

the second semiconductor layer is formed on the substrate layer, and thedrain electrode and the source electrode are constructed on the secondsemiconductor layer;

the second semiconductor layer and a first semiconductor layer body arecombined to form a heterojunction channel, and the two ends of theheterojunction channel are connected with the drain electrode and thesource electrode respectively; the thickness of the first semiconductorlayer body is not greater than the critical thickness of 2DEG formed onthe heterojunction channel, and thus natural 2DEG in the heterojunctionchannel is depleted;

the first semiconductor layer comprises a body and n parts ofprotrusions grown along the body, wherein n≥1;

the dielectric template layer is arranged on the first semiconductorlayer body and provided with n windows, and the n parts of protrusionsare grown along the n windows; through the protrusions, the thickness ofthe first semiconductor layer exceeds the critical thickness, so that2DEG is formed in the projection regions of the protrusions, and n partsof 2DEG regions are formed on the heterojunction channel at intervals;

the gate electrode is arranged on the first dielectric layer.

In certain specific implementation schemes, the novel III-Vheterojunction field effect transistor is a normally off III-Vheterojunction field effect transistor and comprises a substrate layer,a second semiconductor layer, a dielectric template layer, a drainelectrode, a source electrode, a first dielectric layer, seconddielectric layers and a gate electrode, wherein,

the second semiconductor layer is formed on the substrate layer, and thedrain electrode and the source electrode are constructed on the secondsemiconductor layer;

the first semiconductor layer comprises a body and n parts ofprotrusions grown along the body, wherein n≥1;

the second semiconductor layer and the first semiconductor layer bodyare combined to form a heterojunction channel, and the two ends of theheterojunction channel are connected with the drain electrode and thesource electrode respectively; the thickness of the first semiconductorlayer body is not greater than the critical thickness of 2DEG formed onthe heterojunction channel, and thus natural 2DEG in the heterojunctionchannel is depleted;

the dielectric template layer is arranged on the first semiconductorlayer body and provided with n windows, and the n parts of protrusionsare grown on the first semiconductor layer body along the n windows;through the protrusions, the thickness of the first semiconductor layerexceeds the critical thickness, so that 2DEG is formed in the projectionregions of the protrusions, and n parts of 2DEG regions are formed onthe heterojunction channel at intervals;

the first dielectric layer is further arranged on the surface of thefirst semiconductor layer, the gate electrode is arranged on the firstdielectric layer and covers the channel in the full length direction,and the two edges of the gate electrode extend out of the edges of thesides, close to the channel, of the drain electrode and the sourceelectrode respectively; the second dielectric layers are arrangedbetween the gate electrode and the drain electrode as well as betweenthe gate electrode and the source electrode.

In certain specific implementation schemes, a dielectric wall isdistributed at least between two adjacent windows in the dielectrictemplate layer and is only distributed in an area which can be coveredby the projection of the gate electrode, the number of the dielectricwalls is n, n≥1, and the dimension of at least one dielectric wall inthe gate width direction is equal to or greater than the gate width; theprotrusions are grown on the first semiconductor layer body along theouter sides of the dielectric walls; through the protrusions, thethickness of the first semiconductor layer exceeds the criticalthickness, so that 2DEG is formed in the projection regions of theprotrusions, and at least two discontinuous 2DEG regions, namely theconnected parts of the edges of the source electrode and the drainelectrode, are formed on the heterojunction channel;

the gate electrode is arranged on the first semiconductor layer and onlycovers two-dimensional electron gas interruption parts in the wholeheterojunction channel.

Compared with the prior art, the novel III-V heterojunction field effecttransistor provided by the present application has the advantages ofsimpler structure, simpler preparation flows, stabler performance,higher reliability and the like.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a sectional view of a conventional enhancement-mode III-V HFETdevice in the prior art;

FIG. 2 is a sectional view of a novel enhancement-mode III-Vheterojunction field effect transistor of the present application;

FIG. 3 is a top view of the novel enhancement-mode III-V heterojunctionfield effect transistor of the present application;

FIG. 4 is a sectional view of a novel enhancement-mode III-Vheterojunction field effect transistor of the present application;

FIG. 5 is a front view of a first semiconductor part, a secondsemiconductor part and a dielectric template part of the novelenhancement-mode III-V heterojunction field effect transistor of thepresent application when n=3, and m=1;

FIG. 6 is a left view of the first semiconductor part, the secondsemiconductor part and the dielectric template part of the novelenhancement-mode III-V heterojunction field effect transistor of thepresent application when n=3, and m=1;

FIG. 7 is a top view of the first semiconductor part, the secondsemiconductor part and the dielectric template part of the novelenhancement-mode III-V heterojunction field effect transistor of thepresent application when n=3, and m=1;

FIG. 8 is a sectional view of a enhancement-mode III-V heterojunctionfield effect transistor structurally provided with a composite barrierlayer of the present application;

FIG. 9 is a front view of a first semiconductor part, a secondsemiconductor part and a dielectric wall part of the enhancement-modeIII-V heterojunction field effect transistor structurally provided withthe barrier layer in the present application when n=3, and m=2;

FIG. 10 is a left view of the first semiconductor part, the secondsemiconductor part and the dielectric wall part of the enhancement-modeIII-V heterojunction field effect transistor structurally provided withthe barrier layer in the present application when n=3, and m=2; and

FIG. 11 is a top view of the first semiconductor part, the secondsemiconductor part and the dielectric wall part of the enhancement-modeIII-V heterojunction field effect transistor structurally provided withthe barrier layer in the present application when n=3, and m=2.

DETAILED DESCRIPTION OF THE INVENTION

Through a continuous and deep study on the structure of an HFET devicein the prior art, the inventor of the present application realizes thatas the thickness of a barrier layer, namely the thickness of a firstsemiconductor layer, of the conventional device exceeds the criticalthickness, high-concentration 2DEG exists on a heterojunction interface,namely the interface between the first semiconductor layer and a secondsemiconductor layer, due to piezoelectric polarization and spontaneouspolarization of the material system under the condition that no externalvoltage is applied. Special techniques such as the trench gate techniqueand the F⁻ ion implantation and doping technique have to be adopted forobtaining an enhancement-mode device. All the techniques have thedefects of difficult accurate control and prolonged technologicalcycles; in addition, for a trench gate structure, the etching techniqueis adopted in the technological process, a channel of the device isdamaged, consequentially, the performance of the device is affected, andpotential hazards exist in the reliability of the device. The F⁻ ionimplantation technique cannot achieve accurate control easily and haspotential hazards in the reliability.

On account of the defects of the existing HFET device, the inventor ofthe present application provides the technical scheme of the presentapplication through long-term study and mass practice, and the technicalscheme is explained and illustrated in detail as follows.

One embodiment of the present application provides a novel III-Vheterojunction field effect transistor which is an enhancement-modeIII-V heterojunction field effect transistor and comprises a substratelayer, a second semiconductor layer, a first semiconductor layer, adrain electrode, a source electrode, a first dielectric layer, seconddielectric layers and a gate electrode, wherein,

the second semiconductor layer is formed on the substrate layer, thedrain electrode and the source electrode are constructed on the secondsemiconductor layer, and the drain electrode and the source electrodeare connected through the first semiconductor layer and are in Ohmiccontact with the first semiconductor layer, so that a channel is formed;compared with the second semiconductor layer, the first semiconductorlayer has a greater bandgap;

the second semiconductor layer and the first semiconductor layer arecombined to form a heterostructure; the thickness of the firstsemiconductor layer is not greater than the critical thickness of 2DEGformed on the heterostructure, and thus natural 2DEG in theheterostructure is depleted;

the first dielectric layer is further arranged on the surface of thefirst semiconductor layer, the gate electrode is arranged on the firstdielectric layer and covers the channel in the full length direction,and the two edges of the gate electrode extend out of the edges of thesides, close to the channel, of the drain electrode and the sourceelectrode respectively; the second dielectric layers are arrangedbetween the gate electrode and the drain electrode as well as betweenthe gate electrode and the source electrode.

Preferably, the second dielectric layers are only located on the edges,overlapping with the drain electrode and the source electrode, of thegate electrode.

Preferably, an intermediate layer used for improving the mobility oftwo-dimensional electron gas on the heterojunction interface is furtherarranged between the first semiconductor layer and the secondsemiconductor layer.

Preferably, the thickness of the intermediate layer can be about 1 nm.

Preferably, the intermediate layer is an AlN layer.

Preferably, the first semiconductor layer is an AlGaN layer or an AlNlayer.

Preferably, the second semiconductor layer is a GaN layer.

For example, in certain implementation schemes, the first semiconductorlayer is an AlGaN layer, and the thickness of the first semiconductorlayer is smaller than or equal to 5 nm and preferably is 1˜5 nm; thesecond semiconductor layer is a GaN layer, and the thickness of thesecond semiconductor layer can be any suitable numerical value such as 2μm.

For example, in certain specific implementation schemes, the firstsemiconductor layer is an AlN layer, and the thickness of the firstsemiconductor layer is 5 nm; the second semiconductor layer is a GaNlayer, and the thickness of the second semiconductor layer is 2 μm.

Preferably, the first dielectric layer is a Si₃N₄ layer which is grownin situ when a heterostructure material is grown, and the thickness ofthe first dielectric layer is 5˜25 nm.

Preferably, a third dielectric layer is further arranged between thegate electrode and the first dielectric layer and used for furtherdecreasing leakage currents of the gate electrode of the device.

Preferably, each second dielectric layer comprises a SiO₂ layer. Incertain specific implementation schemes, the thickness of eachdielectric layer can be 100 nm.

Preferably, the edges of the sides, towards the channel, of the seconddielectric layers are beyond the drain electrode and the sourceelectrode respectively by the length of 0˜2 μm and preferably by thelength of 0.5 μm.

Preferably, the distance between the drain electrode and the sourceelectrode can be about 2.5 μm.

According to the novel enhancement-mode III-V heterojunction fieldeffect transistor provided in the above embodiment of the presentapplication, the depleted channel is obtained through a thin barrierlayer, an MIS gate structure is adopted, 2DEG is induced again by meansof high gate voltage, and thus the enhancement-mode device with stableperformance is realized.

In certain more specific implementation schemes of the above embodiment,the structure of the novel enhancement-mode III-V heterojunction fieldeffect transistor is shown in FIG. 2 and FIG. 3, wherein FIG. 2 is asectional view of the device, and FIG. 3 is a top view of the device.

Wherein, the novel enhancement-mode III-V heterojunction field effecttransistor comprises a substrate layer 1, a second semiconductor layer2, a first semiconductor layer 3, a drain electrode 4, a sourceelectrode 5, a first dielectric layer 6, second dielectric layers 7 anda gate electrode 8, wherein,

the second semiconductor layer 2 is formed on the substrate layer 1, thedrain electrode 4 and the source electrode 5 are constructed on thesecond semiconductor layer 2, and the drain electrode 4 and the sourceelectrode 5 are connected through the first semiconductor layer 3 andare in Ohmic contact with the first semiconductor layer 3, so that achannel is formed; compared with the second semiconductor layer 2, thefirst semiconductor layer 3 has a greater bandgap;

the second semiconductor layer 2 and the first semiconductor layer 3 arecombined to form a heterostructure; the thickness of the firstsemiconductor layer 3 is not greater than the critical thickness of 2DEGformed on the heterostructure, and thus natural 2DEG in theheterostructure of the first semiconductor layer 3 is depleted; thefirst semiconductor layer of a thin structure is designed, and thethickness of the first semiconductor layer is smaller than the criticalthickness, so that the high-concentration 2DEG naturally exists on theheterostructure is eliminated; in this way, in the absence of anexternal gate voltage, no 2DEG exists on the heterojunction interface ofthe first semiconductor layer and the second semiconductor layer,high-concentration 2DEG can be induced from the channel only when anexternal gate voltage exceeds a certain positive threshold voltage, anenhancement-mode form is formed, and accordingly the process for formingthe enhancement-mode device is greatly simplified.

The first dielectric layer 6 is further arranged on the surface of thefirst semiconductor layer 3, the gate electrode 8 is arranged on thefirst dielectric layer 6 and covers the channel in the full lengthdirection, and the two edges of the gate electrode 8 extend out of theedges of the sides, close to the channel, of the drain electrode 4 andthe source electrode 5 respectively; the second dielectric layers 7 arearranged between the gate electrode 8 and the drain electrode 4 as wellas between the gate electrode 8 and the source electrode 5. As the gateelectrode structurally covers the channel completely, 2DEG in thechannel can be completely controlled by the gate voltage, and the devicefree of current collapse is realized.

In one preferred embodiment, the second dielectric layers 7 are onlylocated on the edges, overlapping with the drain electrode 4 and thesource electrode 5, of the gate electrode 8. The second dielectriclayers 7 are used for preventing electrical connection between the gateelectrode 8 and the drain electrode 4 as well as between the gateelectrode 8 and the source electrode 5, however, the second dielectriclayers 7 also have an influence on the gate capacitance, and then thegate control capacity and the amplifying capacity are affected. Comparedwith a structure that a second dielectric layer completely covers afirst dielectric layer, the structure that the second dielectric layers7 only cover the edges, overlapping with the drain electrode 4 and thesource electrode 5, of the gate electrode 8 can ensure a greater gatecapacitance on the premise of achieving good electrical isolation, ahigher device transconductance is realized, and the device has highergate control capacity and greater amplifying capacity. Preferably, thethicknesses of the second dielectric layers should be as small aspossible, so that the second dielectric layers are extremely thin underthe orthographic projection of the gate electrode, and the loss of thegate capacitance is minimized.

Meanwhile, the realizing technique for the novel enhancement-mode III-Vheterojunction field effect transistor is basically the same as thetechnique for the HFET in the prior art, and the technique complexity ofthe device is not increased at all. The device of the presentapplication can be realized through the following main technologicalsteps:

(1) Growth of a substrate material, specifically, a corresponding bufferlayer, the second semiconductor layer, the first semiconductor layer andan in-situ Si₃N₄ layer are grown on the suitable substrate material(such as an Si substrate) according to the material growth law, and theintermediate layer is selectively grown on the substrate material.

(2) Cleaning of the substrate material, specifically, a proper cleaningscheme is adopted, and thus a clean material surface is obtained;

(3) Preparation of the source electrode and the drain electrode.

(4) Growth of the second dielectric layers.

(5) Etching of selected zones of the second gate dielectric layers.

(6) Preparation of the gate electrode.

(7) Passivating and packaging.

In the above embodiment of the present application, by adoption of thetechnical scheme, the technique complexity of the device is notincreased at all, the threshold voltage can be set by setting parameterssuch as the thickness of the first semiconductor layer and the thicknessof the first dielectric layer, repeatability of the technique for thedevice is achieved, and industrial production of the device isfacilitated.

The novel enhancement-mode III-V heterojunction field effect transistorprovided in one embodiment of the present application is a normally offIII-V heterojunction field effect transistor and comprises a substratelayer, a first semiconductor layer, a second semiconductor layer, adielectric template layer, a drain electrode, a source electrode, afirst dielectric layer, second dielectric layers and a gate electrode,wherein,

the second semiconductor layer is formed on the substrate layer, and thedrain electrode and the source electrode are constructed on the secondsemiconductor layer;

the first semiconductor layer comprises a body and n parts ofprotrusions grown along the body, wherein n≥1;

the second semiconductor layer and the first semiconductor layer bodyare combined to form a heterojunction channel, and the two ends of theheterojunction channel are connected with the drain electrode and thesource electrode respectively; the thickness of a first semiconductorlayer body is not greater than the critical thickness of 2DEG formed onthe heterojunction channel, and thus natural 2DEG in the heterojunctionchannel is depleted;

the dielectric template layer is arranged on the first semiconductorlayer body and provided with n windows at equal intervals, and the nparts of protrusions are grown on the first semiconductor layer bodyalong the n windows; through the protrusions, the thickness of the firstsemiconductor layer exceeds the critical thickness, so that 2DEG isformed in the projection regions of the protrusions, and n 2DEG regionsare formed on the heterojunction channel at equal intervals.

The first dielectric layer is further arranged on the surface of thefirst semiconductor layer, the gate electrode is arranged on the firstdielectric layer and covers the channel in the full length direction,and the two edges of the gate electrode extend out of the edges of thesides, close to the channel, of the drain electrode and the sourceelectrode respectively; the second dielectric layers are arrangedbetween the gate electrode and the drain electrode as well as betweenthe gate electrode and the source electrode.

Preferably, the protrusions are distributed continuously or are dividedinto m parts in the growth direction, wherein m≥1.

Preferably, the second dielectric layers are only located on the edges,overlapping with the drain electrode and the source electrode, of thegate electrode.

Preferably, an intermediate layer used for improving the mobility oftwo-dimensional electron gas on the heterojunction interface is furtherarranged between the first semiconductor layer and the secondsemiconductor layer.

Preferably, the intermediate layer is an AlN layer.

Preferably, the first semiconductor layer is an AlGaN layer or an AlNlayer, and the second semiconductor layer is a GaN layer.

Preferably, the first dielectric layer is a Si₃N₄ layer which is grownin situ when a heterostructure material is grown, and the thickness ofthe first dielectric layer is 5˜25 nm.

Preferably, the dielectric template layer comprises a SiO₂ layer such asa SiO₂ layer grown through LPCVD.

Preferably, each second dielectric layer is a SiO₂ layer.

Preferably, the edges of the sides, towards the channel, of the seconddielectric layers are beyond the drain electrode and the sourceelectrode respectively by the length of 0.5 μm.

According to the novel normally off III-V heterojunction field effecttransistor provided in the above embodiment of the present application,the discontinuous channel is obtained through a specially designedbarrier layer, and 2DEG is induced again through a high gate voltage, sothat the normally off device with stable performance is realized, andflexible and diversified design schemes can be adopted according to theperformance requirement of the device.

In certain more specific implementation schemes of the above embodiment,the structure of the novel enhancement-mode III-V heterojunction fieldeffect transistor is shown in FIG. 4, FIG. 5, FIG. 6 and FIG. 7, whereinFIG. 4 is a sectional view of the device, FIGS. 5 and 6 are three viewsof the first semiconductor part, the second semiconductor part and thedielectric template part when n=2, and m=1 respectively, FIG. 5 is aleft view, FIG. 6 is a front view, and FIG. 7 is a top view. The novelnormally off III-V heterojunction field effect transistor of the presentapplication comprises a substrate layer 1, a second semiconductor layer2, a first semiconductor layer body 3, first semiconductor layerprotrusions 9, two-dimensional electron gas 10, a dielectric templatelayer 11, a first dielectric layer 6, second dielectric layers 7, a gateelectrode 8, a drain electrode 4 and a source electrode 5.

Wherein, the second semiconductor layer 2 is formed on the substratelayer 1, the drain electrode 5 and the source electrode 4 areconstructed on the second semiconductor layer 2, the first semiconductorlayer body 3 is formed on the second semiconductor layer 2, and thefirst semiconductor layer body 3 and the second semiconductor layer 2are combined to form a heterojunction channel; the drain electrode 5 andthe source electrode 4 are connected through a channel formed betweenthe first semiconductor layer body 3 and the second semiconductor layer2; compared with the second semiconductor layer, the first semiconductorlayer has a greater bandgap; the thickness of the first semiconductorlayer body 3 is not greater than the critical thickness of 2DEG formedon the heterostructure.

The dielectric template layer 6 is constructed on the firstsemiconductor layer body 3 and provided with n windows at equalintervals, and the n parts of protrusions 4 are grown on the firstsemiconductor layer body 3 along the n windows; through the protrusions,the thickness of the first semiconductor layer exceeds the criticalthickness, so that 2DEG is formed in the projection regions of theprotrusions, and n 2DEG regions are formed on the heterojunction channelat equal intervals.

If only the first semiconductor layer body 3 exists, 2DEG cannot begenerated in the heterostructure; due to the presence of the firstsemiconductor layer protrusions 4, the total thickness of the firstsemiconductor layer body 3 and the first semiconductor layer protrusions4 is greater than the critical thickness for generating 2DEG and thus2DEG exists on the heterojunction interface below the firstsemiconductor layer protrusions 4. Accordingly, discontinuous 2DEG isdistributed on the heterojunction interface. As the 2DEG isdiscontinuous, no conductive channel is formed in the absence of a gatevoltage, and the HFET device is normally off. The 2DEG on theheterojunction interface can be continuous only when the gate voltage isgreater than a threshold voltage, and thus the conductive channel isformed.

By adoption of the above technical scheme, the gate electrode of thedevice completely covers the channel between the source electrode andthe drain electrode, so that when the device operates, the gate voltagecan completely control the channel, instant on-off of the channel isachieved, and thus current collapse can be avoided to the maximumextent.

In addition, although the gate electrode of the device covers thechannel between the source electrode and the drain electrode,two-dimensional electron gas exists on the first semiconductor layerprotrusions always, the equivalent gate length of the device only equalsto the length of the total protrusions of the first semiconductor layer,and thus the device has a high cut-off frequency. Meanwhile, as thebreakdown voltage of the device is in positive correlation with thedistance between the source electrode and the drain electrode, thedevice can also have a high breakdown voltage.

The first dielectric layer 6 is further arranged on the surface of thefirst semiconductor layer, the gate electrode 8 is arranged on the firstdielectric layer 6 and covers the channel in the full length direction,and the two edges of the gate electrode 8 extend out of the edges of thesides, close to the channel, of the drain electrode 4 and the sourceelectrode 5 respectively; the second dielectric layers 7 are arrangedbetween the gate electrode 8 and the drain electrode 4 as well asbetween the gate electrode 8 and the source electrode 5. As the gateelectrode structurally covers the channel completely, 2DEG in thechannel can be completely controlled by the gate voltage, and the devicefree of current collapse is realized.

In a preferred embodiment, in the direction perpendicular to theconnection direction of the source electrode and the drain electrode,the first semiconductor layer protrusions 9 can be distributedcontinuously and can also be divided into m parts. The dielectrictemplate 6 is discontinuous in the direction from the source electrodeto the drain electrode.

In a preferred embodiment, the second dielectric layers 7 are onlylocated on the edges, overlapping with the drain electrode 5 and thesource electrode 4, of the gate electrode 8. The second dielectriclayers 7 are used for preventing electrical connection between the gateelectrode 8 and the drain electrode 5 as well as between the gateelectrode 8 and the source electrode 4, however, the second dielectriclayers 7 also have an influence on the gate capacitance, and then thegate control capacity and the amplifying capacity are affected. Comparedwith a structure that a second dielectric layer completely covers afirst dielectric layer, the structure that the second dielectric layers7 only cover the edges, overlapping with the drain electrode 5 and thesource electrode 4, of the gate electrode 8 can ensure a greater gatecapacitance on the premise of achieving good electrical isolation, agreater device transconductance is realized, and the device has highergate control capacity and higher amplifying capacity. Preferably, thethicknesses of the second dielectric layers should be as small aspossible, so that the second dielectric layers are extremely thin underthe orthographic projection of the gate electrode, and the loss of thegate capacitance is minimized.

Meanwhile, the realizing technique for the novel enhancement-mode III-Vheterojunction field effect transistor is basically the same as thetechnique for the HFET in the prior art, and the technique complexity ofthe device is not increased at all. The device of the presentapplication can be realized through the following main technologicalsteps:

(1) Growth of a substrate material, specifically, a corresponding bufferlayer, the second semiconductor layer, the first semiconductor layerbody 3 and the dielectric template layer 6 are grown on the suitablesubstrate material (such as a Si substrate) according to the materialgrowth law, and the intermediate layer is selectively grown on thesubstrate material.

(2) Formation of the windows grown along the first semiconductor layerprotrusions 9 through photolithography and etching of the dielectrictemplate layer.

(3) Growth of the first semiconductor layer protrusions 9.

(4) Preparation of the source electrode and the drain electrode.

(5) Growth of the first dielectric layer.

(6) Growth of the second dielectric layers and etching in selectedregions.

(7) Preparation of the gate electrode.

(8) Passivation.

In the above embodiment of the present application, by adoption of thetechnical scheme, the normally off device can be realized; as thechannel material of the device is obtained through growing instead ofetching adopted for a trench gate device, damage to the heterojunctioninterface is avoided, and thus the performance of the device can beimproved easily.

The novel III-V heterojunction field effect transistor provided in oneembodiment of the present application is a normally off III-Vheterojunction field effect transistor structurally provided with acomposite barrier layer and comprises a substrate layer, a secondsemiconductor layer, dielectric walls (also regarded as dielectrictemplate layers of another form), a drain electrode, a source electrodeand a gate electrode, wherein,

the second semiconductor layer is formed on the substrate layer, and thedrain electrode and the source electrode are constructed on the secondsemiconductor layer;

the second semiconductor layer and the first semiconductor layer bodyare combined to form a heterojunction channel, and the two ends of theheterojunction channel are connected with the drain electrode and thesource electrode respectively; the thickness of the first semiconductorlayer body is not greater than the critical thickness of 2DEG formed onthe heterojunction channel, and thus natural 2DEG in the heterojunctionchannel is depleted.

The dielectric walls are arranged on the first semiconductor layer bodyand are only distributed in the area which can be covered by theprojection of the gate electrode, the number of the dielectric walls isn, n≥1, and the dimension of at least one dielectric wall in the gatewidth direction is equal to or greater than the gate width; protrusionsare grown on the first semiconductor layer body along the outer sides ofthe dielectric walls; through the protrusion, the thickness of the firstsemiconductor layer exceeds the critical thickness, so that 2DEG isformed in the projection regions of the protrusions, and at least twodiscontinuous 2DEG regions, namely the connected parts of the edges ofthe source electrode and the drain electrode, are formed on theheterojunction channel at equal intervals.

The gate electrode is arranged on the first semiconductor layer and onlycovers two-dimensional electron gas interruption parts in the wholeheterojunction channel.

In certain implementation schemes of the above embodiment, the firstdielectric layer is further arranged between the gate electrode and thefirst semiconductor layer.

In certain implementation schemes of the above embodiment, theprotrusions are distributed continuously in the area covered by theprojection of the gate electrode or are divided into m parts in thegrowth direction, wherein m≥1.

In certain implementation schemes of the above embodiment, anintermediate layer which is used for improving the mobility of 2DEG onthe heterojunction interface is further arranged between the firstsemiconductor layer and the second semiconductor layer.

The intermediate layer is, but not limited to, an AlN layer.

In certain implementation schemes of the above embodiment, the firstsemiconductor layer can be, but is not limited, to an AlGaN layer, anAlN layer and the like.

In certain implementation schemes of the above embodiment, the secondsemiconductor layer can be, but is not limited to, a GaN layer.

In certain implementation schemes of the above embodiment, the firstdielectric layer is a Si₃N₄ layer which is grown in situ when aheterostructure material is grown. Preferably, the thickness of thefirst dielectric layer is 5˜25 nm.

In certain implementation schemes of the above embodiment, n windows areformed on the dielectric walls through the photolithography and etchingtechnique.

A specific implementation scheme of the above embodiment is shown inFIGS. 8 to 11 and relates to the enhancement-mode III-V heterojunctionfield effect transistor structurally provided with the composite barrierlayer (called the device for short in the following description). FIG. 8is a sectional view of the device, FIGS. 9 to 11 are three views of thefirst semiconductor part, the second semiconductor part and thedielectric wall part when n=2 and m=2, FIG. 9 is a front view, FIG. 10is a left view, and FIG. 11 is a top view. Furthermore, the devicecomprises a substrate layer 1, a second semiconductor layer 2, a firstsemiconductor layer body 3, first semiconductor layer protrusions 9,two-dimensional electron gas 10, dielectric template layer 11, a firstdielectric layer 6, a gate electrode 8, a source electrode 5 and a drainelectrode 4.

Wherein, the second semiconductor layer 2 is formed on the substratelayer 1, the drain electrode 4 and the source electrode 5 areconstructed on the second semiconductor layer 2, the first semiconductorlayer body 3 is formed on the second semiconductor layer 2, and thefirst semiconductor layer body 3 and the second semiconductor layer 2are combined to form a heterostructure; the drain electrode 5 and thesource electrode 4 are connected through a channel formed between thefirst semiconductor layer body 3 and the second semiconductor layer 2;compared with the second semiconductor layer, the first semiconductorlayer has a greater bandgap; the thickness of the first semiconductorlayer body 3 is not greater than the critical thickness of 2DEG formedon the heterostructure.

The dielectric layer is constructed on the first semiconductor layerbody 3, the dielectric template layer 11 are constructed through thephotolithography or and etching technique, and the protrusions 9 aregrown on the first semiconductor layer body 3 along the outer sides ofthe dielectric walls; through the protrusions, the thickness of thefirst semiconductor layer exceeds the critical thickness, so that 2DEGis formed in the projection regions of the protrusions, and 2DEG regionsare formed on the heterojunction channel at intervals.

If only the first semiconductor layer body 3 exists, 2DEG cannot begenerated in the heterostructure; due to the presence of the firstsemiconductor layer protrusions 9, the total thickness of the firstsemiconductor layer body 3 and the first semiconductor layer protrusions9 is greater than the critical thickness for generating 2DEG and thus2DEG exits on the heterojunction interface below the first semiconductorlayer protrusions 9. Accordingly, discontinuous 2DEG is distributed onthe heterojunction interface. As the 2DEG is discontinuous, noconductive channel is formed in the absence of a gate voltage, and theHFET device is normally off. The 2DEG on the heterojunction interfacecan be continuous only when the gate voltage is greater than a thresholdvoltage, and thus the conductive channel is formed.

In the above embodiment of the present application, the dielectric wallsare only distributed in the area covered by the projection of the gateelectrode, namely the first semiconductor layer protrusions are grown onthe connected parts of the drain electrode and the source electrode, sothat 2DEG is formed on the parts, close to the source electrode and thedrain electrode, of the heterojunction channel, and on-off state of theheterojunction channel can be controlled only by covering the 2DEGinterruption parts in the whole heterojunction channel with the gateelectrode, Therefore, for the device in the above embodiment, the gateelectrode does not need to be isolated from the drain electrode or thesource electrode through dielectric layers, the production technique isgreatly simplified, and meanwhile, the breakdown voltage of thetransistor is greatly improved.

In one preferred embodiment, the first dielectric layer 6 is furtherarranged on the surface of the first semiconductor layer, the gateelectrode 8 is arranged on the first dielectric layer 6, the gateelectrode 8 covers the two-dimensional electron gas interruption partsin the whole composite barrier layer, and thus it is ensured that thesource electrode and the drain electrode are connected through 2DEG whena certain gate voltage is applied to the device.

In one preferred embodiment, in the direction perpendicular to theconnection direction of the source electrode and the drain electrode,the first semiconductor layer protrusions 9 can be distributedcontinuously and can also be divided into m parts. The device can bedesigned extremely flexibly. Meanwhile, the realizing technique for thenovel enhancement-mode III-V heterojunction field effect transistor isbasically the same as the technique for the HFET in the prior art, andthe technique complexity of the device is not increased at all. Thedevice of the present application can be realized through the followingmain technological steps:

(1) Growth of a substrate material, specifically, a corresponding bufferlayer, the second semiconductor layer and the first semiconductor layerbody 3 are grown on the suitable substrate material (such as an Sisubstrate) according to the material growth law, an intermediate layeris selectively grown on the substrate material, and dielectric layersrequired by the dielectric walls 11′ are constructed.

(2) Formation of the dielectric template layer 11 throughphotolithography and etching on the dielectric layers;

(3) Growth of the first semiconductor layer protrusions 9.

(4) Preparation of the source electrode and the drain electrode.

(5) Growth of the first dielectric layer.

(6) Preparation of the gate electrode.

(7) Device passivation.

By adoption of the above technical scheme, the normally off device canbe realized; in addition, as the channel material of the device isobtained through growing instead of etching adopted for a trench gatedevice, damage to the heterojunction interface is avoided, and theperformance of the device can be improved.

According to the normally off III-V heterojunction field effecttransistor structurally provided with the composite barrier layerprovided in the above embodiment of the present application, thediscontinuous channel is obtained through the specially designed barrierlayer, 2DEG is induced again through a high gate voltage, and thus thenormally off device with the stable performance is realized. Inaddition, flexible and diversified design schemes can be adoptedaccording to the performance requirement of the device. Meanwhile, sincethe gate electrode only covers the two-dimensional electron gasinterruption parts in the whole heterojunction channel, the breakdownvoltage of the transistor is greatly improved.

A further description of the of the technical scheme of the invention isgiven with several preferred embodiments and corresponding accompanyingdrawings as follows, however, the present application is not limited tothe embodiments.

First Embodiment

For a novel enhancement-mode III-V heterojunction field effecttransistor in the embodiment, a substrate material comprises a Simaterial and a low-temperature AlN buffer layer grown on the Simaterial, a second semiconductor layer (with the thickness of about 2μm) is a GaN layer, a first semiconductor layer (with the thickness ofabout 1˜5 nm) is an AlGaN layer, and an AlN intermediate layer (with thethickness of about 1 nm) is arranged between the first semiconductorlayer and the second semiconductor layer and used for improving theelectrical property of 2DEG A first dielectric layer is a Si₃N₄ layerwhich is grown in situ, and the thickness of the first dielectric layeris about 5˜25 nm. A source electrode and a drain electrode are allformed by Ti/Al/Ni/Au (20/120/50/200 nm) through metal deposition andhigh-temperature thermal annealing, and the distance between the sourceelectrode and the drain electrode is 2.5 μm. Each second dielectriclayer is a SiO₂ layer, and the thickness of each second dielectric layeris about 100 nm. The edges of the sides, towards the center of achannel, of the second dielectric layers are beyond the source electrodeand the drain electrode respectively by the length of 0.5 μm. A gateelectrode is prepared from Ni/Au (50/150 nm). The preparation process ofthe device comprises the following steps that firstly, thelow-temperature AlN buffer layer is grown on the substrate materialcontaining Si then the second semiconductor layer which is a GaN layeris grown, then the first semiconductor AlGaN layer is grown, and a Si₃N₄layer is grown in situ to serve as the first dielectric layer; secondly,the first dielectric layer at the position of the source electrode andthe drain electrode is etched, and Ohmic contact is prepared; thirdly,the second dielectric layers are grown, and the second dielectric layersare only left on the edges of the source electrode and the drainelectrode through photolithography and etching; and finally, the gateelectrode is prepared.

Second Embodiment

For a novel enhancement-mode III-V heterojunction field effecttransistor in the embodiment, a substrate material comprises a SiCmaterial and a low-temperature AlN layer grown on the SiC material, asecond semiconductor layer (with the thickness of about 2 μm) is a GaNlayer, a first semiconductor layer (with the thickness of about 5 nm) isan AlN layer, a first dielectric layer is a Si₃N₄ layer which is grownin situ, and the thickness of the first dielectric layer is about 5-25nm. A source electrode and a drain electrode are all formed byTi/Al/Ni/Au (20/120/50/200 nm) through metal deposition andhigh-temperature thermal annealing, and the distance between the sourceelectrode and the drain electrode is 2.5 μm. Each second dielectriclayer is a SiO₂ layer, and the thickness of each second dielectric layeris about 100 nm. The edges of the sides, towards the center of achannel, of the second dielectric layers are beyond the source electrodeand the drain electrode respectively by the length of 0.5 μm. A gateelectrode is prepared from Ni/Au (50/150 nm).

Third Embodiment

For a novel normally off III-V heterojunction field effect transistor inthe embodiment, a substrate material comprises a Si material and alow-temperature AlN buffer layer grown on the Si material, a secondsemiconductor layer (with the thickness of about 2 μm) is a GaN layer,the first part (with the thickness of about 3 nm) of a firstsemiconductor layer is an AlGaN layer, an AlN intermediate layer (withthe thickness of about 1 nm) is arranged between the first semiconductorlayer and the first part of the second semiconductor layer and used forimproving the electrical property of 2DEG. A dielectric template layeris a SiO₂ layer which is grown through low-pressure chemical vapordeposition (LPCVD). n, the number of windows on the dielectric templatelayer is two, then m is one. The length of each window in the connectiondirection of a source electrode and a drain electrode is 0.5 μm, and thelength of each window in the direction perpendicular to the direction ofthe connection direction of the source electrode and the drain electrodeis 100 μm. A first dielectric layer is a Si₃N₄ layer which is grown insitu, and the thickness of the first dielectric layer is about 10 nm;each second dielectric layer is an hfO₂ layer, and the thickness of eachsecond dielectric layer is 100 nm. The source electrode and the drainelectrode are all formed by Ti/Al/Ni/Au (20/120/50/200 nm) through metaldeposition and high-temperature thermal annealing. The distance betweenthe source electrode and the drain electrode is 2.5 μm. The edges of thesides, towards the center of a channel, of the second dielectric layersare beyond the source electrode and the drain electrode respectively bythe length of 0.5 μm. A gate electrode is prepared from Ni/Au (50/150nm). The preparation process of the device comprises the following stepsthat firstly, the low-temperature AlN buffer layer is grown on the Sisubstrate material, then the second semiconductor layer which is a GaNlayer is grown, then the body part of the first semiconductor AlGaNlayer is grown, then the dielectric template layer which is a SiO₂ layeris grown through low-pressure chemical vapor deposition (LPCVD),dielectric walls are reserved through photoeching and etchingtechniques, the secondary epitaxial windows are exposed, then thematerial is placed into a material growing device again, and protrusionsof the first semiconductor layer are grown again in the windows;secondly, a Si₃N₄ layer is grown in situ to serve as the firstdielectric layer; thirdly, the first dielectric layer at the positionsof the source electrode and the drain electrode is etched, and ohmiccontact is prepared; fourthly, the second hfO₂ dielectric layers aregrown, and the second dielectric layers are only left on the edges ofthe source electrode and the drain electrode through photoechingphotolithography and etching; and finally, the gate electrode isprepared.

Fourth Embodiment

For a novel normally off III-V heterojunction field effect transistor inthe embodiment, a substrate material comprises a SiC material and alow-temperature AlN buffer layer grown on the SiC material, a secondsemiconductor layer (with the thickness of about 2 μm) is a GaN layer,and the first part (with the thickness of about 3 nm) of a firstsemiconductor layer body is an AlN layer. A dielectric template layer isa SiO₂ layer which is grown through LPCVD, the number n of windows onthe dielectric template layer is two, then m is three, the length ofeach window in the connection direction of a source electrode and adrain electrode is 0.5 μm, and the length of each window in thedirection perpendicular to the direction of the connection direction ofthe source electrode and the drain electrode is 20 μm. A firstdielectric layer is a Si₃N₄ layer which is grown in situ, and thethickness of the first dielectric layer is about 10 nm; each seconddielectric layer is an hfO₂ layer, and the thickness of each seconddielectric layer is 100 nm. The source electrode and the drain electrodeare all formed by Ti/Al/Ni/Au (20/120/50/200 nm) through metaldeposition and high-temperature thermal annealing. The distance betweenthe source electrode and the drain electrode is 2.5 μm. The edges of thesides, towards the center of a channel, of the second dielectric layersare beyond the source electrode and the drain electrode respectively bythe length of 0.5 μm. A gate electrode is prepared from Ni/Au (50/150nm).

Fifth Embodiment

For the novel enhancement-mode III-V heterojunction field effecttransistor structurally provided with a composite barrier layer in theembodiment, a substrate material comprises a Si material and alow-temperature AlN buffer layer grown on the Si material, a secondsemiconductor layer (with the thickness of about 2 μm) is a GaN layer,the body part (with the thickness of about 3 nm) of a firstsemiconductor layer is AlN, an AlN intermediate layer (with thethickness of about 1 nm) is arranged between the second semiconductorlayer and the body part of the first semiconductor layer and used forimproving the electrical property of 2DEG each dielectric wall is a SiO₂layer which is grown through low-pressure chemical vapor deposition(LPCVD), the number n of the dielectric walls is two, then the number mof protrusions is one, the length of a window in the connectiondirection of a source electrode and a drain electrode is 0.5 μm, and thelength of the window in the direction perpendicular to the connectiondirection of the source electrode and the drain electrode is 100 μm. Afirst dielectric layer is a Si₃N₄ layer which is grown in situ, and thethickness of the first dielectric layer is about 10 nm. The sourceelectrode and the drain electrode are all formed by Ti/Al/Ni/Au(20/120/50/200 nm) through metal deposition and high-temperature thermalannealing. The distance between the source electrode and the drainelectrode is 2.5 μm. A gate electrode is prepared from Ni/Au (50/150nm).

Six Embodiment

For the novel enhancement-mode III-V heterojunction field effecttransistor structurally provided with a composite barrier layer in theembodiment, a substrate material comprises a SiC material and alow-temperature AlN buffer layer grown on the SiC material, a secondsemiconductor layer (with the thickness of about 2 μm) is a GaN layer,and the first part (with the thickness of about 3 nm) of a firstsemiconductor layer is an AlN layer. Each dielectric wall is a SiO₂layer which is grown through LPCVD, the number n of the dielectric wallis one, then the number m of the protrusion is one, the length of awindow in the connection direction of a source electrode and a drainelectrode is 0.5 μm, and the length of the window in the directionperpendicular to the connection direction of the source electrode andthe drain electrode is 20 μm. A first dielectric layer is a Si₃N₄ layerwhich is grown in situ, and the thickness of the first dielectric layeris about 10 nm. The source electrode and the drain electrode are allformed by Ti/Al/Ni/Au (20/120/50/200 nm) through metal deposition andhigh-temperature thermal annealing. The distance between the sourceelectrode and the drain electrode is 2.5 μm. A gate electrode isprepared from Ni/Au (50/150 nm).

The above embodiments are only used for assisting in understanding themethod and the core concept of the present application. It should bepointed out that various improvements and modifications of the presentapplication made by those ordinary in the field without deviating fromthe principle of the present application are also within the protectionscope of the claims of the present application. The modifications of theembodiments are obvious for those skilled in the field, and the generalprinciple defined by the present application can be realized in otherembodiments without deviating from the spirit or the scope of thepresent application. Therefore, the present application is not limitedto the embodiments provided above and can be as wide as possible toinclude all embodiments consistent with the principle and novelcharacteristics disclosed by the present application.

What is claimed is:
 1. A novel III-V heterojunction field effecttransistor, characterized by comprising a substrate layer, a secondsemiconductor layer, a first semiconductor layer, a drain electrode, asource electrode, a first dielectric layer, second dielectric layers anda gate electrode, wherein, the second semiconductor layer is formed onthe substrate layer, the second semiconductor layer and the firstsemiconductor layer are combined to form a heterostructure, the firstsemiconductor layer has a greater bandgap compared with the secondsemiconductor layer, the drain electrode and the source electrode areconstructed on the second semiconductor layer, and the drain electrodeand the source electrode are connected through the first semiconductorlayer and are in Ohmic contact with the first semiconductor layer, sothat a channel is formed; the thickness of the first semiconductor layeris not greater than the critical thickness of 2DEG formed on theheterostructure, and thus natural 2DEG in the heterostructure isdepleted; the first dielectric layer is further arranged on the surfaceof the first semiconductor layer, the gate electrode is arranged on thefirst dielectric layer and covers the channel in the full lengthdirection, and the two edges of the gate electrode extend out of theedges of the sides, close to the channel, of the drain electrode and thesource electrode respectively; the second dielectric layers are arrangedbetween the gate electrode and the drain electrode as well as betweenthe gate electrode and the source electrode.
 2. The novel III-Vheterojunction field effect transistor according to claim 1,characterized in that the second dielectric layers are only located onthe edges, overlapping with the drain electrode and the sourceelectrode, of the gate electrode.
 3. The novel III-V heterojunctionfield effect transistor according to claim 1, characterized in that anintermediate layer used for improving the mobility of two-dimensionalelectron gas on the heterojunction interface is further arranged betweenthe first semiconductor layer and the second semiconductor layer, andpreferably, the intermediate layer is an AlN layer.
 4. The novel III-Vheterojunction field effect transistor according to claim 1,characterized in that the first semiconductor layer is an AlGaN layer oran AlN layer, and the second semiconductor layer is a GaN layer.
 5. Thenovel III-V heterojunction field effect transistor according to claim 1,characterized in that the thickness of the first semiconductor layer issmaller than 5 nm and preferably is 1˜5 nm.
 6. The novel III-Vheterojunction field effect transistor according to claim 1,characterized in that the first dielectric layer is a Si₃N₄ layer whichis grown in situ when a heterostructure material is grown, and thethickness of the first dielectric layer is 5˜25 nm.
 7. The novel III-Vheterojunction field effect transistor according to claim 1,characterized in that a third dielectric layer is further arrangedbetween the gate electrode and the first dielectric layer.
 8. The novelIII-V heterojunction field effect transistor according to claim 1,characterized in that each second dielectric layer is a SiO₂ layer. 9.The novel III-V heterojunction field effect transistor according toclaim 1, characterized in that the edges of the sides, towards thechannel, of the second dielectric layers are beyond the drain electrodeand the source electrode respectively by the length of 0˜2 μm.
 10. Anovel III-V heterojunction field effect transistor, characterized bycomprising a substrate layer, a first semiconductor layer, a secondsemiconductor layer, a dielectric template layer, a drain electrode, asource electrode, a first dielectric layer, second dielectric layers anda gate electrode, wherein, the second semiconductor layer is formed onthe substrate layer, and the drain electrode and the source electrodeare constructed on the second semiconductor layer; the secondsemiconductor layer and the first semiconductor layer body are combinedto form a heterojunction channel, and the two ends of the heterojunctionchannel are connected with the drain electrode and the source electroderespectively; the thickness of the first semiconductor layer body is notgreater than the critical thickness of 2DEG formed on the heterojunctionchannel, and thus natural 2DEG in the heterojunction channel isdepleted; the first semiconductor layer comprises a body and n parts ofprotrusions grown along the body, wherein n≥1; the dielectric templatelayer is arranged on the first semiconductor layer body and providedwith n windows, and the n parts of protrusions are grown along the nwindows; through the protrusions, the thickness of the firstsemiconductor layer exceeds the critical thickness, so that 2DEG isformed in the projection regions of the protrusions, and n 2DEG regionsare formed on the heterojunction channel at intervals; the gateelectrode is arranged on the first dielectric layer.
 11. The novel III-Vheterojunction field effect transistor according to claim 10,characterized in that the two edges of the gate electrode extend out ofthe edges of the sides, close to the channel, of the drain electrode andthe source electrode respectively; the second dielectric layers arearranged between the gate electrode and the drain electrode as well asbetween the gate electrode and the source electrode respectively. 12.The novel III-V heterojunction field effect transistor according toclaim 10, characterized in that the dielectric template layer isarranged on the first semiconductor layer body and provided with nwindows at equal intervals, and n 2DEG regions are formed on theheterojunction channel at equal intervals.
 13. The novel III-Vheterojunction field effect transistor according to claim 10,characterized in that in the gate length direction, a dielectric wall isdistributed between at least two adjacent widows in the dielectrictemplate layer, and the dimension of at least one dielectric wall in thegate width direction is equal to or greater than the gate width; theprotrusions are grown on the first semiconductor layer body along theouter sides of the dielectric walls; through the protrusion, thethickness of the first semiconductor layer exceeds the criticalthickness, so that 2DEG is formed in the projection regions of theprotrusions, and at least two discontinuous 2DEG regions, namely theconnected parts of the edges of the source electrode and the drainelectrode, are formed on the heterojunction channel; the gate electrodeonly covers the two-dimensional electron gas interruption parts in thewhole heterojunction channel.
 14. The novel III-V heterojunction fieldeffect transistor according to claim 10, characterized in that theprotrusions are distributed continuously or divided into m parts in thegrowth direction, and m≥1.
 15. The novel III-V heterojunction fieldeffect transistor according to claim 10, characterized in that thesecond dielectric layers are only located on the edges, overlapping withthe drain electrode and the source electrode, of the gate electrode. 16.The novel III-V heterojunction field effect transistor according toclaim 10, characterized in that an intermediate layer used for improvingthe mobility of 2DEG on the heterojunction interface is further arrangedbetween the first semiconductor layer and the second semiconductorlayer, and preferably, the intermediate layer is an AlN layer.
 17. Thenovel III-V heterojunction field effect transistor according to claim10, characterized in that the first semiconductor layer is an AlGaNlayer of an AlN layer, and the second semiconductor layer is a GaNlayer.
 18. The novel III-V heterojunction field effect transistoraccording to claim 10, characterized in that the first dielectric layeris further arranged on the surface of the first semiconductor layer, andthe gate electrode is arranged on the first dielectric layer.
 19. Thenovel III-V heterojunction field effect transistor according to claim18, characterized in that the first dielectric layer is a Si₃N₄ layerwhich is grown in situ when a heterostructure material is grown, and thethickness of the first dielectric layer is 5˜25 nm.
 20. The novel III-Vheterojunction field effect transistor according to claim 10,characterized in that the dielectric template layer or each seconddielectric layer is a SiO₂ layer.